1. Field of the Invention
The present invention relates to a reverse-flow prevention device for a fuel tank of an automobile which is provided between a fuel filler port and the fuel tank in the automobile.
2. Prior Art
Conventionally, a reverse-flow prevention device for a fuel tank, which has a function to open a filler pipe when fuel flows normally during supply of the fuel and to close the filler pipe when the fuel spits back to flow reversely, comprises component parts such as a valve body, one valve disc, a rotational axis pin and so on, which are manufactured independently of one another. This type of reverse-flow prevention device requires such work as to flatten the top end of the rotational axis pin so that it may not be disconnected after the rotational axis pin is assembled at a bearing portion for the valve disc.
In the case where the reverse-flow prevention valve for the fuel tank comprises one valve disc, it is necessary to locate the reverse-flow prevention valve at the attachment position where the direction of the valve is so controlled that the reverse-flow prevention valve may operate correctly. More particularly, the valve body is provided with locating projections and the pipe to be connected includes locating recesses, and by engaging the projections of the valve body with the recesses of the pipe, the direction of the valve is set optimumly. This is for the purpose of directing the valve in such direction that it is always closed by its own weight, thereby ensuring quick response of the valve when the fuel flows reversely and making the resistance against the fuel as little as possible when it is supplied. Alternatively, in a state that the valve disc is closed, when the rotational axis pin of the bearing portion is cohered with burning tar material or foreign matters so that there occurs a rotational failure of the valve disc, it may be impossible to supply the fuel to the automobile.
Further, the fuel flows turbulently in a filler pipe during being supplied. This is one cause for deteriorating an efficiency of feeding the fuel. Accordingly, it is preferable to introduce the fuel in a laminar flow.
In order to feed the fluid in the filler pipe stably in a state like as the laminar flow, such type of reverse-flow prevention device is also applicable that two valve discs having generally half-circular shapes are used and closed by force of springs (for example, U.S. Pat. No. 4,867,199). However, when the fuel flows only through the lower half of the filler pipe, the fuel flow cannot be rectified sufficiently by means of the valve discs owing to an unfavorable attachment angle of the valve discs, even in the case where the valve discs are two. Moreover, since the valve discs are required to be opened against the force of the springs, this type of device has a disadvantageous point such that the resistance against the fuel flow is increased.